Hours after Nevada disallowed fighters from therapeutic-use exemptions for testosterone, Ultimate Fighting Championship middleweight title challenger Vitor Belfort of Brazil withdrew from his scheduled May 24 championship shot at Chris Weidman. Former light-heavyweight champion Lyoto Machida will now fight Weidman at the MGM Grand. The 36-year-old Belfort (24-10), who last had a title shot against then-middleweight champion Anderson Silva in 2011 and has fought in the UFC since 1997, has used testosterone replacement therapy (TRT)

Men over 65, as well as younger men with diagnosed heart disease, were at least twice as likely to have non-fatal heart attacks in the 90 days after they were prescribed testosterone medication than were men of the same age and health status who did not get the hormone supplement, a study has found. For men under 65 with no diagnosis of cardiovascular disease, testosterone supplementation did not appear to raise heart attack risk, the study suggests. But among men older than 65, many of whom may have had undiagnosed risk factors, rates of non-fatal heart attack rose as much as threefold in the 90 days after they filled a prescription for testosterone medication.

Could you have low testosterone? That's the question Abbott Laboratories (now AbbVie) has been urging men to consider with its "Is It Low T?" awareness campaign, a highly effective effort to change how doctors and the public think about managing aging in men. Since 2008, this massive marketing endeavor has targeted middle-aged men who have put on some weight, sometimes feel grumpy or get sleepy after meals, encouraging them to have their testosterone...

World Boxing Assn. and International Boxing Federation junior welterweight champion Lamont Peterson has tested positive for synthetic testosterone, jeopardizing his May 19 title defense against England's Amir Khan at Mandalay Bay in Las Vegas, said Keith Kizer, executive director of the Nevada State Athletic Commission, and Peterson's promoter, Richard Schaefer. Kizer and Schaefer confirmed the positive result for synthetic testosterone and are now awaiting a letter Tuesday explaining the result from Peterson's attorney, both men said.

Hormonally speaking, becoming a father may make you less of a man, according to new research that finds testosterone levels drop in men after they become parents. But fear not for manhood — the results show that men are evolutionarily wired to help raise their children and that testosterone may get in the way, scientists say. Testosterone is a hormone associated with perceived hallmarks of masculinity such as libido, aggression and musculature. Those can be useful qualities when competing for a mate, but less so when raising a child — an endeavor that requires calm, attentiveness and an even temper.

What makes a corporate merger go bad? Is it a dramatic change in stock price? A revelation about an unprofitable business unit? Resistance from federal regulators? Researchers from the University of British Columbia propose another explanation – too much testosterone . Maurice Levi, Kai Li and Feng Zhang of the university’s Sauder School of Business came up with their theory based on prior research showing that the male sex hormone affects the way men play the ultimatum game . In one version of this game, Player A was asked to divide up $40 between himself and Player B – he could choose either a $35-$5 split, or a $15-$25 split.

A chemical found in plastics has been shown to increase testosterone levels in men, British researchers reported on Wednesday. They found that men who had high levels of the chemical bisphenol A also had higher testosterone levels compared to men with lower levels of the chemical in their bodies. The chemical, also known as BPA, is commonly found in plastic products around the world. The new study comes on the heels of research released earlier this month that found high amounts of BPA are present in everyday cash register receipts , as much as 3% of the total weight of the receipt.

San Francisco Giants outfielder Melky Cabrera has been suspended 50 games without pay after testing positive for testosterone, Major League Baseball said Wednesday. According to the commissioner's office, Cabrera violated the league's joint drug prevention and treatment program by testing positive for the banned substance and his suspension will begin immediately. “My positive test was the result of my use of a substance I should not have used,” Cabrera said in a statement released by the players' union.

Testosterone, the hormone that drives male aggression and sexual interest, also seems able to boost short-term success at finance. But elevated testosterone levels over several days could lead to irrational risk-taking, researchers at the University of Cambridge in England reported Tuesday in the Proceedings of the National Academy of Sciences. The team studied male financial traders in London, taking saliva samples in the morning and evening. Those with higher levels of testosterone in the morning were more likely to make an unusually big profit that day.

Men over 65, as well as younger men with diagnosed heart disease, were at least twice as likely to have non-fatal heart attacks in the 90 days after they were prescribed testosterone medication than were men of the same age and health status who did not get the hormone supplement, a study has found. For men under 65 with no diagnosis of cardiovascular disease, testosterone supplementation did not appear to raise heart attack risk, the study suggests. But among men older than 65, many of whom may have had undiagnosed risk factors, rates of non-fatal heart attack rose as much as threefold in the 90 days after they filled a prescription for testosterone medication.

Georges St-Pierre said Tuesday the lack of stringent drug testing for mixed martial arts fighters contributed to his decision to take an indefinite leave as Ultimate Fighting Championship welterweight champion. In an interview with reporters in Montreal, St-Pierre in a story published by Canadian Press said the absence of a uniform drug-testing policy up to his satisfaction “bothered me greatly. It was one of the reasons I decided to step aside.” St-Pierre, who endured sometimes brutal punishment in November to successfully defend his welterweight belt against Johny Hendricks by split-decision in Las Vegas, originally wanted Hendricks to participate in drug testing overseen by the Las Vegas-based Voluntary Anti-Doping Assn.

LAS VEGAS - Vitor Belfort said he hurts for injured countryman Anderson Silva, but has a plan to gain a measure of Brazilian revenge as the next opponent for Ultimate Fighting Championship middleweight champion Chris Weidman. “The belt's in the hands of a guy named Chris Weidman, but it belongs to me,” Belfort said late Saturday at the MGM Grand following the horrific lower-left-leg injury suffered by Silva in the second round of the UFC 168 title fight. Silva, 38, underwent emergency surgery to treat the broken leg he suffered when kicking Weidman's left shin in the second round.

Trust science on this: Guys are generally not eager to mate with a high-testosterone bearded lady. But what goes on with other animals that share “male” ornamentation? Do the females pay a heavy price for aping the decoration of their sexual counterparts? If so, why would that trait survive? PHOTOS: Weird sea creatures and strange fish The eastern fence lizard may offer some answers, according to a study published online Tuesday in the journal Biology Letters.

Human nature being what it is, people are going to have extramarital and intra-office affairs, and no amount of warning from friends, Scriptures or made-for-cable movies will prevent them. But anyone in a position of power to hire and fire is inviting more than just personal trouble when getting involved with an employee. That's especially true when the affair involves an elected official and an aide. Residents want to know that the staffers trying to solve their problems are being promoted or demoted based on their policy expertise, not because of their fling with the boss.

Testosterone is powerful--in the male human body and in the American pharmacological marketplace. From 1993 to 2000, prescriptions for testosterone replacements increased fivefold, boosted by advertising campaigns that invited aging men to "talk to their doctor about low T" if they were experiencing decreased energy, sex drive or muscle tone. Until now, however, physicians haven't really known just how low testosterone levels might produce these...

Dodgers fans are still celebrating the 50-game suspension of San Francisco Giants star Melky Cabrera for using a banned substance, which could very well end the Giants' hopes of defeating Los Angeles for the National League West title. But there's no joy in Bay City. The San Francisco Chronicle reports that even the Giants players have turned against Cabrera, casting serious doubt on whether he will ever again appear in an orange-and-black uniform. What's less clear is whether they're mad at him for cheating, or mad at him for cheating so inexpertly.

Weekly injections of the hormone testosterone can reduce sperm counts to zero in 98.6% of men, providing the first effective male contraceptive, according to a report from a World Health Organization team in the April issue of Fertility and Sterility. That effectiveness is equal to the efficacy of oral contraceptives for women.

Smaller testicle size in men appears to be linked to greater involvement in child rearing, according to Georgia researchers. The study , published recently in the journal PNAS, was conducted by anthropologists at Emory University in Atlanta and involved 70 local fathers ages 21 to 43. The study participants, who were recruited with fliers and Facebook advertisements, all had children who were 1 or 2 years old. Researchers measured the...

August 13, 2013 | By Melissa Healy, This post has been corrected. See below for details.

If you're a middle-aged guy who watches sports, news or late-night talk shows, you've seen the ads: Your flagging energy levels, mood, sports prowess and libido ... could they be caused by low T? After you figure out that T stands for "testosterone" -- a magically powerful male hormone the shortage of which you would never want to admit to -- you say to yourself, "Oh my God, maybe it is low T!" And if you then go to the website mentioned in the ads and take a quiz, you'll quickly learn that there is a treatment for low T, one that you can ask your doctor about.